When using autoconf macros, one has to be careful because some
arguments as they may need additional escaping. In this
particular case, the second argument passed to
AC_DEFINE_UNQUOTED() is problematic as autoconf runs it in a
subshell resulting in 'yes' being interpreted as a name of a
variable instead of literal "yes" string. Putting quotes around
it lets shell know we want string comparison.

This problem was noticed with autoconf-2.71.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Acked-by: Tom Hromatka <tom.hromatka@oracle.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>